All conventional flippers suffer from a series of problems, in particular:
1) Deformation of the Flipper During Swimming
All conventional flippers, during the swimming movement, are subject to deformation which does not allow ideal channelling of the fluid flows. In fact, as schematically shown in FIG. 1 of the accompanying drawings, only one component F1 of the thrust produced by the flipper P is positive, while there is always a vertical component F2 which represents a loss in efficiency.
During a flipper movement against the direction of flow or when the diver must perform strong flipper movements, for example when in a very negative postural condition or when a high speed is required, deformation of the flipper P increases, as schematically shown in FIG. 2, resulting in a further increase in the loss of efficiency F2 and a consequent reduction of the active component F1.
On the market there therefore exist “rigid” flippers which are normally used by more demanding and expert divers and which, when a strong thrust is required, do not bend excessively and therefore ensure a good performance in these conditions.
On the other hand, these flippers require a considerable amount of force and well-trained leg muscles. Moreover, during the flipper movement performed in normal swimming conditions, they do not bend enough and therefore do not generate a good thrust.
Conversely, flippers which are too “soft” will function well during a supple flipper swimming action, but will bend too much in more stressful conditions, as shown in FIG. 3 where it can be seen that the component F1 is practically zero, while the component F2 prevails.
2) Angle of Attack
Since the human foot forms an angle with the leg, if flippers with a “flat” fin, i.e. fin extending along the plane of the foot sole, were to be used, a very poor efficiency during the downwards movement would be obtained.
For some time now, flipper manufacturers have adopted the special measure of inclining the flipper fin a few degrees in order to obtain a better angle of attack, in particular during a downwards flipper swimming movement.
This angle, however, is the result of a compromise since it cannot be too pronounced otherwise there would be a loss of efficiency during the upwards flipper swimming movement.
In order to improve this aspect, European patent No. 1127589 in the name of the same Applicant proposes a flipper with a pivoting fin and with an angular movement controlled by a number of mechanical constraints, able to achieve a far more favourable angle of attack during the two flipper swimming movements.
This solution undoubtedly increases the efficiency of the flipper, but does not solve the problem described under point 1.
3) Thrust “Dead” Zones
During the alternating movement of the flipper, the latter must pass from optimum deformation in one direction to deformation in the opposite direction, when the leg movement is reversed. In order to pass from one deformed condition into the other a certain amount of time is required. During this time period the flipper provides practically no thrust. Two “dead” angles, as indicated by a negative sign in FIG. 4, therefore occur during the flipper movement. In order to be able to reduce these angles, various solutions have been used. The solution used in European patent No. 1127589 mentioned above, owing to the hinge which allows a certain freedom of movement of the fin, is also able to minimize these dead angles, as graphically shown in the diagram of FIG. 5. In this case also, however, the problem described under point 1 is not solved.
4) Channelling of the Fluid Flow
In order to improve the efficiency of the flippers, systems which are able to better channel the fluid flow have been developed so as to displace a greater quantity of water in the direction of the movement. The problem with these flippers, however, arises during slow swimming and, in particular, when subject to considerable forces since, being a relatively “soft” flipper, the latter deforms excessively with a consequent loss of thrust and efficiency.
5) Fatigue During Swimming
All the technical solutions described above tend, in particular, to improve the efficiency of the flipper. In fact, the most important characteristic to be achieved is that of maximum thrust with minimum effort. In this respect the thrust which may be obtained by “normal size” flippers cannot be increased beyond a certain value and also the maximum speed which can be obtained with a flipper cannot exceed certain values, also because the resistance of the water increases with the square of the speed.
It is therefore important to have a compact flipper which produces a good thrust, but which requires the minimum amount of effort possible during both slow and fast swimming. This means, in the case of free divers, that they are able to spend more time underwater and, in the case of scuba divers using autonomous breathing equipment, that they are able to spend longer periods under water as a result of a smaller air consumption due to less fatigue.
In addition there is less risk of suffering cramps, in particular in the case of divers with lower fitness levels.
The flipper according to the present invention aims to solve all of the abovementioned problems, offering optimum thrust characteristics with a very small amount of effort.
Further advantages which may be obtained with the flipper according to the present invention are as follows:
Possibility of varying the deformation with a consequent change in characteristics from “harder” to “softer”.
Possibility of manufacture using various technologies and constructional solutions so as to provide flippers with different price and performance levels, but all characterized by the same operating principles.
The main object of the invention is therefore to obtain a flipper which, during swimming, is deformed in the manner of an “S”, i.e. with a double bend, instead of a single bend as is the case with all the commercially available flippers. Obviously, this double bend must be present both during the upward movement and during the downward movement, as shown schematically in the accompanying FIGS. 6 and 7.
The advantages of this solution are immediately obvious.
There is no longer the loss of efficiency present in conventional flippers, owing to channelling of the fluid flow in the direction of the movement and acceleration of the same outgoing flow.
The thrust will therefore be greater and the energy required to move the flipper decidedly smaller, owing to the increase in efficiency.
The principle is simple and can be easily understood, but the difficulty is how to obtain this double-bend deformation.
The innovative solution able to achieve this result is that of allowing a part of the flipper, i.e. the more central part, to be deformed under force, while the part furthest from the foot is substantially fastened to the more rigid side ribs or to the fin support structure.
A first solution is that shown schematically in FIG. 8 where the central part of the fin 3 is free to move and is guided, in its terminal zone, by two transverse contact elements 4 and 4′ fixed to the ribs 2.
The result, therefore, is that, during swimming, the central part of the fin 3 will tend to flex easily, while the terminal part 3′, which is forced to slide inside the transverse guides 4, 4′ fixed to the ribs 2, will bend in the opposite direction to the bend formed by the fin 3.
By positioning the transverse guides 4, 4′ at different points along the ribs 2 (as shown schematically in FIG. 9) or by changing the rigidity of the fin 3 or the initial flexing point, two S-shaped curvatures with a substantially different amplitude and shape—and consequent different “hardness” and thrust characteristics of the fin 3—will be obtained.
In a simplified version of the flipper, the fin 33 may be formed as one piece, without the transverse guides, only the central part of the fin 33 being no longer connected to the ribs 2, as schematically shown in FIGS. 10 and 11. An S-shaped deformation of the fin 33 will also be obtained in this case during swimming.
With these technical solutions the problems mentioned under points 1, 2 and 3 are brilliantly solved.
In order to solve also the problem of channelling of the fluid flow it is sufficient to add deformable folding side pockets 6 which will be able not only to ensure a good “channel effect” but also to operate as deformation limiters for the central part of the fin 3 or 33 (FIGS. 12 and 13).
Obviously the materials used for the fin and shoe of the flipper may vary greatly, from thermoplastic rubbers to engineering polymers, composites and combinations of all these or other materials or technological manufacturing solutions such as overmoulding or mechanical assembly of the flipper components, without, however, departing from the scope of protection of the present invention.